Fluid pressure producing device



P. H. MISTRAL 2,185,264

FLUID PRESSURE PRODUCING DEVICE Filed Feb. 26, 19:57 4 Sheets-Sheet 1 Jan. 2, 1940*.

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Jan. 2, 1940. P.'H. MISTRAL FLUID PRESSURE PRODUCING DEVICE Filed Feb. 26. 1957 4 Sheefs-Sheei 2 Unven't'z m' PM If. Masha attorney Jam. 2 WW. P. H. MISTRAL FLUID PRESSURE PRODUCING DEVICE 4 Sheets-Sheet 3 can w ATTORNEY.-

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Y B emu Q3 Q2 E N8 m& u v vi NE rr Q3 NQ m s m & Q, s. 3 n g 6T7! fl Hll .0 m2 mv M v r 0% Uv k Jan. 2, 1940. P. H. MISTRAL FLUID "PRESSURE rnopucme DEVICE 4 Sh eet s- Sheet 4 Filed Feb. 26. 1937 Pal HJlIwraL Patented Jan. 2, 11940 UNITED STATES rum) rrmssuac rnopocmc DEVICE Paul Henri Mistral, Paris,

Bendix Aviation Corporation,

a company France, assignor to South Bend, Iud.,

Application February 26, 1937, Serial No. 127,839% In France August 26, 1936 4 Claims.

This invention relates to fluid pressure producing devices and is concerned more particularly with master cylinders adapted to be used for the actuation of hydraulic brake systems for motor vehicles.

In order to secure quickly, with minimum motion and effort, the highest possible fluid pressure for a given actuating force applied to the fluid pressure producing device, the latter embodies a low pressure producing means having a large capacity to do the light work of taking up the clearance, overcoming flexibilities and the like inherent in the fluid pressure responsive mechanism, and a high pressure producing means to do the heavy work and permitting the application of high working pressure upon a substantial part of movement of the control pedal or lever.

One of the objects of the present invention is to provide a smooth transition from the stage of low pressure to the stage of high pressure.

Another object of the invention is to provide a fluid pressure producing device including a low pressure producing means and a high pressure producing means adapted to be operated simul-- taneously to apply an initial pressure on the fluid, whereby upon increase of pressure applied to the fluid the communication between the low pressure producing means and the high pressure producing means is repeatedly cut ofi and reestablished gradually to step up the pressure applied on the fluid. v

A further object of the invention is to provide a fluid pressure producing device including a low pressure cylinder having a piston and a. high pressure cylinder having a piston, the transition from the stage of low pressure to the stage of high pressure taking place upon a relative movement between the two pistons.

Still another object of the invention is to provide a fluid pressure producing device including a low pressure piston and a coaxial high pressure piston, said pistons being arranged in such a manner that upon increase of pressure upon the fluid one piston is displaced with respect to the other to transfer gradually the pressure to the fluid.

A still further object of the invention is to provide a fluid pressure producing device including a low pressure cylinder having a piston and a high pressure cylinder having a piston, said pistons being arranged to permit the disconnecting of the low pressure cylinder upon a relative movement between the two pistons.

Other objects and advantages oi the invention will appear from the following description taken in connection with the accompanying drawings, in which- Fig. 1 is a vertical section view of one embodiment of the present invention,

Fig. 2 is a similar view of another embodiment of the present invention, showing however the various parts in brake applying position,

Fig. 3 is a view in section of still another embodiment;

Fig. 3A is a section corresponding to Fig. 3 showing the parts in their operated positions,

Fig. 4 is a top view of the embodiment shown in Fig.3,

Fig. 5 is a view similar to Fig. 3 and shows a further embodiment,

Figure 5A is a section corresponding to Fig. 5

showing the parts in their operated positions, and

Fig. 6 is a top view 'of the embodiment shown in Fig. 5. Referring to the drawings -for more specific details of the invention, the compression device is formed by a double bore casting l0 forming a low pressure cylinder I! of comparatively large volume and a high pressure cylinder H of comparatively small volume. In the low pressure cylinder i2 is adapted to reciprocate a big diameter piston l6 engaged on its periphery by a sealing gasket I8. The piston |6 adapted to operate as a low pressure piston is formed with .a sleeve 20 having a diameter corresponding to the bore of the high pressure cylinder I4 and adapted to reciprocate in the latter. In the sleeve 20 are formed ports 22 and 24 which in normal position provide a communication between the low pressure cylinder l2 and the high pressure cylinder l4.

The low pressure piston is formed with a central bore in which is mounted a small diameter .piston 26 adapted to operate as a high pressure piston. The piston 26 is engaged on its periphery by a sealing gasket 28. In the embodiment shown in Fig. 1 the low pressure piston I6 is shown as being formed by a cylindrical member at and a sleeve member 12 interlocked by a key M.

The high pressure piston 26 is formed with an annular groove 3% into which engages a ball 38 loaded by a spring 40. a This spring loaded ball 38 forms a yielding driving connection between the two pistons. The spring 40 loading the ball 38 is mounted in a bore closed by a screw l2 and the load of the spring taking support on the screw 42 can be adjusted by rotating the latter.

' able fluid, upon actuation of the brake pedal or lever a thrust is transmitted to the coupling 44 in the direction of the arrow F, resulting in moving simultaneously both the pistons on the compressive stroke. The fluid forced by the two pistons passes into the discharge chamber .48, and then into a fluid pressure delivery pipe connected thereto to be directed to the fluid pressure responsive devices such as the wheel cylinders not shown on the drawings.

During the initial movement of the pistons, the

fluid compressed in the low pressure cylinder I2 is forced therefrom through the ports 22 and 24 into the discharge chamber 48. Then, due to the advance of the sleeve 20, the ports 24 come below the plane 50 and are covered by the wallof the high pressure cylinder I4. The fluid is then forced from the low pressure cylinder I2 through the ports 22.

As the pressure on the fluid has attained a value equal to the resistance of the connection between the two pistons formed by the spring loaded ball 38, the ball is pushed backwards, the two pistons separate one from another, and

the high pressure piston 28 continues alone its compressive stroke. This forward movement of the piston 26 closes the ports 22 and the low pressure cylinder I2 is then completely shut 05.

As the high pressure piston 26 continues its forward stroke, the pressure increases in the discharge chamber. Owing to the small area of this piston a substantially small efiort applied to the control lever or pedal permits the obtaining of a substantially high pressure in the discharge chamber and in the fluid pressure responsive devices connected thereto.

In the event of the master cylinder according to the present invention being used for actuating a hydraulic brake system of a motor car, the common movement of both the pistons can be used to take up the clearance between the brake shoes and the brake drums, and the movement of the small diameter piston 28 is used to apply the final braking pressure.

It will be observed that, as the pressure increases in the discharge chamber I4, said pressure reacts on the head ofthe sleeve 28, and causes a backward movement of the low pressure piston I8 which prevents a sudden passage from the low pressure stage to the high pressure stage. This construction enables the pressure applied to the fluid to be stepped up gradually so that a progressive transition takes place from the low pressure stage to the high pressure stage.

Should the effort applied to the high pressure piston be of such an extent as to createan important increase of pressure in the discharge chamber 48, this pressure reacting on the head of the sleeve 20 will shift backwards the piston I6, against the resistance of the spring 46, So as to uncover the ports 24. A communication is then re-established between the high pressure cylinder I4 and the low pressure cylinder I2, which communication is again out ofl due to the increase of load on the spring 46 which becomes compressed under the action of the effort which continues to act on the coupling 44 causing a forward movement of the piston I6. The ports 24 then come again below the plane 50 and are covered by the wall of the high pressure cylinder I4 and this repeated cutting ofi and establishing communication between the low pressure cylinder and the high pressure cylinder permits an extremely smooth transition from low pressure to high pressure without any detrimental jerk taking place.

As the effort acting on the coupling 44 is relieved, the high pressure piston returns to normal position under the action of the spring 46. When the high pressure piston, in returning, reaches its original position relative to the low pressure piston the two pistons are interlocked by the spring loaded ball 38, and the two pistons thereafter move as a unit to their fully released positions, and the master cylinder is ready to operate again.

The cylinder can be connected to a fluid reservoir not shown on the drawings by means of I a fitting 5| controlled by a valve, which can be formed-by a spring loaded ball 52. The areas of'the piston.26 and the end of the sleeve 20 and the strength of the spring 46 as well as the strength of the spring 40 are proportioned so that the resulting pressure during the high pressure operation, the pedal pressure required during both the low pressure and high pressure oper ation and the time of change-over from low pressure to high pressuremost nearly approach the desired characteristics for the operation of the brakes or other operated mechanism.

It will be observed from the foregoing that the fluid pressure producing device according to the invention presents the advantage consisting in that the application of increased pressure is realised without having recourse either to valve means or to locking means,- which are expensive and are often subject to disa'djustment.

In the subsequent embodiments similar parts are designated by similar reference numerals, and the operation 01' said embodiments is identical to that described above.

The embodiment shown in Fig. 2 is in all respects similar to that illustrated in Fig. 1, except that the discharge chamber 48 is connected to a distribution casing 54 from which four conduits 56 lead to respective pressure reas by means of an aperture I88 formed in said casing. The low pressure piston H8 is formed with a sleeve I20 having a diameter corresponding to the bore of the flange I82 projecting from the fixed casing I88, and carries a head I42. The high pressure piston I28 has a diameter corresponding to that of the sleeve I 28. A relatively strong spring I 84 is inserted between a head I68, formed-on the high pressure piston I28, and the low pressure piston I IS. A weaker spring I88 is inserted between the head I82 and a seat I10 formed on the casing I58 to assist the return of the low pressure piston. In normal position a communication is provided between the low pressure cylinder H2 and the high pressure cylinder II4.by means of ports I22. Various sealing gaskets I12, I14, I16, I18 and I are provided to ensure a suitable sealing action. The high pressure piston H8 is shown as being formed with a pull rod I82 connected to a manually operated control lever or pedal.

A fluid pressure responsive piston I84 is sleeved 5 on the casing I58 and is adapted to be displaced in the direction of the arrow F as pressure is applied to the fluid. The piston I84 is formed with a yoke I86 operatively connected to the vehicle brake hook up so that the movement of 10 the piston I84 in the direction of the arrow F causes an application of the vehicle brakes.

In operation, a pull exerted on the manually operated rod I82 results in moving the piston I28 connected to said rod as well as of the piston 15 H6 which is displaced through the intermediary of the spring I64. During the initial movement of the two pistons the fluid compressed in the low pressure cylinder H2 is forced through the ports I22 into the high pressure cylinder H4.

20 the fluid pressure being transmitted to the pressure responsive piston I84.

As the pressure on the fluid has attained a value corresponding to the resistance of the spring I84 the latter is compressed, and the 26 high pressure piston I28 is then'displaced with respect to the low pressure piston H8 closing the ports I 22' provided in the sleeve I28. The low pressure chamber H2 is thus shut off and the high pressure pistonI28 is then alone operative 80 to apply pressure on the pressure responsive piston I84. Since the area of thehigh pressure piston I28 is much smaller than that of the pressure responsive piston I 84 a small pull applied to the rod I82 permits the application of 8!! a substantially high pressure to the piston I84- and to the brake hook up connected thereto. It appears from thc foregoing that the brake amplifier according to the present invention permits the manual effort applied to the brake pedal to 40 be substantially increased, thus eliminating the need of any servo-mechanism or booster.

The device illustrated in the Figures 5, 5A and 6 is in all respects similar to that shown in Figures 3, 3A and 4, except that the low pressure 5 piston is normally interconnected with the high pressure piston by means of balls 238 engaged in a groove 238 formed on the periphery of the high pressure piston 228. The balls 238 are inserted between two conical surfaces formed on 5 washers 288 and 298 respectively abutting against a shoulder 289 and the spring 292. The spring 292, the, tension of which can be adjusted by means of a nut 294 threaded in the low pressure piston 2H5, acting in conjunction with the co. it. al

55 surfaces of the washers 288 and 298 resiliensy urges the balls 238 into the groove 236. The.

spring 284 is compressed between the low pressure piston and a flat washer 29I abutting against a shoulder 293 formed on the high pressure pisgo ton. i

If desired a lost motion connection can be provided between the manually operated rod I86 and the pressure responsive piston I84 operatively connected to the brake hook up in case the g master cylinder becomes inoperative. As shown in Figures 3 and 4 a pin I98 is secured to the rod I82 and is adapted to engage a member I91 which may be a brake operating lever 'pivotally connected to the piston I84 by means of pins I98 7 and operatively connected to the brake hook up in case of failure of the master cylinder.

Although this invention-has been described in connection with certain specific embodiments the principles involved are susceptible of numerous 7 other applications that will readily occur to persons skilled in the art. The invention is therefore to be limited only as indicated by the scope of the appended claims.

Having thus described the various features of the invention, what I claim as new and desire 5 to secure by Letters Patent is:

1. A fluid pressure producing device comprising a low pressure producing means including a piston, a high pressure producing means including a piston, a spring between said pistons, and means automatically actuated upon the fluid being subjected to pressure and dependent on the fluid pressure acting on both pistons and upon the pressure of the spring between the pistons for establishing and closing communication between the low pressure producing means and the high pressure producing means.

2. A fluid pressure producing device comprising a low pressure cylinder, a low-pressurepiston mounted in the said cylinder, a high pressure cylinder having a diameter smaller than that of the low pressure cylinder, a sleeve connected to the low pressure piston and adapted to reciprocate in the high pressure cylinder, said sleeve defining a bore in the low pressure piston of smaller diameter than the high pressure cylinder, a high pressure piston mounted in the said bore, apertures in the sleeve adapted to provide a communication between the low pressure cylinder and the high pressure cylinder, a yielding driving connection between the pistons permitting a simultaneous displacement of the pistons to apply an initial pressure on the fluid and close one of the apertures provided in the sleeve, said connection being adapted to yield as a predetermined pressure is applied to the fluid to permit the displacement of the high pressure piston for applying an increased pressure on the fluid and close the other aperture provided in the sleeve, whereby the low pressure piston is then adapted to be displaced with respect to the high pressure piston under the action of the pressure acting on the head of the said sleeve to open the first named aperture.

3. A fluid pressure producing device comprising a low pressure cylinder having a piston, a high pressure cylinder having a piston adapted to operate simultaneously with the piston in the first cylinder and having means yieldably and releasably connecting it to the first piston to apply an initial pressure on the fluid and to be disconnected from the latter to apply an increased pressure on the fluid, and a pressure controlling means including two apertures normally providing communication between the low pressure cylinder and the high pressure cylinder, and of which the one is shut off upon simultaneous operation of the two pistons for applying an initial pressure on the fluid and the other is shut ofi upon movement of the high pressure piston inde-- pendently of the low pressure piston, the first aperture being adapted to be reopened upon increase of pressure in the high pressure cylinder, 7

4. A fluid pressure producing device comprising a low pressure cylinder, a low pressure piston having a central bore provided therein, a high pressure cylinder, a high pressure piston mounted in the said bore, a yielding driving connection between the pistons permitting a simultaneous displacement of the pistons to apply an initial pressure on the fluidand adapted to yield upon the increase of the said pressure to permit the displacement of the high pressure piston with re- 7 of the two pistons and with another aperture adapted to be out 01? by the high pressure piston upon its displacement with respect to the low pressure piston.

PAUL HENRI MISTRALQ 

